The present invention generally relates to overhead lighting systems and more particularly to lighting systems that can be used with grid ceilings.
Grid ceilings are widely used, commonly in office buildings. They provide a false or secondary ceiling (also called a “dropped ceiling”) below the structural ceiling of the building and create a plenum space above the secondary ceiling for hiding HVAC ducts, pipes, electrical wiring and the like. In a typical grid ceiling, a T-bar structure suspended from the structural ceiling provides a grid of rectangular openings, commonly 2′ by 2′ or 2′ by 4′ openings, into which ceiling tiles are set to produce a finished ceiling for a space.
Overhead lighting for grid ceiling systems is typically provided in the form of recessed lighting or ceiling suspended lighting fixtures. In the case of recessed lighting, suitably sized rectangular fixtures called “troffers” are placed in selected gird openings of the T-bar grid in the place of ceiling tiles. Recessed troffers typically are relatively deep and cumbersome fixtures that use fluorescent lamps as a light source. They have large bottom fixture openings flush with the grid ceiling that are either uncovered, as in parabolic troffers, or covered by a lens. The recessed troffers provide a pattern of large area sources of light on the ceiling grid.
An example of suspended lighting fixtures in common use with grid ceiling systems are linear fluorescent lighting fixtures, wherein elongated fixtures having a uniform cross-sectional shape are suspended below the ceiling by stems or cables. Suspended linear fluorescent lighting systems can provide direct or indirect lighting, or a combination of both, and typically come in standard length sections, such as 4, 8 or 12 foot sections, that can be suspended beneath the ceiling as stand-alone fixtures or in a system of fixtures joined together by connectors in continuous runs. The stems or cables that suspend the linear fluorescent lighting system are normally tied into the T-bar grid of the grid ceiling at suspension points, and power cords for each section or selected sections are normally dropped through the ceiling to the sections along the suspension cables or the inside of a hollow stem.
In the above-described conventional approaches to providing overhead lighting in spaces with grid ceilings, the overhead lighting is a fixed installation that is relatively labor intensive to install. Such systems cannot be readily modified or re-configured to meet particular or changing application requirements. Also, the light fixtures themselves each provide relatively large lumen packages which illuminate relatively large areas within the space. They do not lend themselves to versatile placement or to the clustering of sources of light for fine tuning lumen placement at particular task and non-task areas within the space. Instead, they follow the conventional lighting design paradigm, which is to uniformly light spaces based on the requirement from the most demanding visual task, resulting in wasted energy through over-lighting of the less visually demanding areas.
Ceiling spot lighting systems are also used to provide lighting within a space. Spot lighting may be built into a ceiling or may be ceiling mounted, such as on ceiling mounted tracks. Spot lighting systems are often used for accent lighting and have no or limited adjustability. In the case of track lighting, positional adjustment of the spot lights is limited to the orientation and range of the track. The tracks can also be unsightly and are not easily installed. Spot lighting can produce excessive shadows and does not provide enough illumination on most vertical surfaces when aimed at illuminating a horizontal work surface. Thus, spot lighting is not generally employed to provide the majority of illumination in an indoor space such as offices, schools, hospitals or retail environments.